I'm pretty sure the ward on the Dursleys' house was a.) specifically targeted for Harry and b.) specific to Voldemort or those influenced by him, due to c.) it drawing on the lingering force of Harry's mother's sacrifice of her life. A similar ward on Hogwarts in general would probably be impractical. (In canon, Harry dies (or intends to die, anyway) in order to protect the greater body of Hogwarts students, and the protection of that magic extends to them, but not as strongly (Voldemort's magic, instead of just bouncing off, does not bind them fully and wears off after a short period of time, viz. Neville and the Body-Bind curse). It might have been possible to make a ward out of this, but it probably wouldn't have been as strong as the already-existing wards, due to that limitation.)